YORKSHIRE WATER KEIGHLEY MOOR DAM EFFICACY …

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YORKSHIRE WATER

KEIGHLEY MOOR DAM EFFICACY ASSESSMENT

MARCH 2012 ________________________________________________

Penny Anderson Associates Limited ‘Park Lea’ 60 Park Road Buxton Derbyshire SK17 6SN

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120108 Penny Anderson Associates Ltd Yorkshire Water2012 Keighley Moor Dam Efficacy Monitoring

1.1 Introduction

Penny Anderson Associated Ltd (PAA) was commissioned by Yorkshire Water in 2010 to design and implement a restoration plan for Keighley Moor which had two key objectives;

to reduce the Dissolved Organic Carbon (DOC) levels in the streams draining from the site;

and in so doing, enhance the blanket bog habitat of the surrounding catchment.

This report assesses the efficacy of the works some 15 months after their installation, whilst still in the defects liability period. It is an abbreviated version of that provided to Yorkshire Water. As it is rare for such a report to be made public, we hope that this helps others to assess and compare the efficacy of their peat dam projects. Leeds University are carrying out detailed hydrological monitoring.

Keighley Moor is an important component of the South Pennines Moors SSSI1 and the site also forms part of the South Pennines SPA/SAC2.

Monitoring the levels of colour in the water at the local treatment works has shown that inflows contain a high level of DOC and also a high colour value. Under AMP 5, actions have been agreed that will attempt to address this through moorland catchment restoration and management rather than through upgrading the treatment works.

The restoration works took place on the moor in winter of 2010-2011 and comprised:

damming suitable gullies to raise the water table;

damming patches of blanket bog vegetation (mostly cottongrass dominated) to reduce the loss of water in peat;

blocking water flows across a burnt area;

re-profiling selected gullies where there are extensive bare peat.

Figure 1 shows the extent of works undertaken in the winter of 2010-2011 overlain on the original gully blocking proposals. There are 693 points where dams and blocks were installed across the moor. (Gullies visible on Figure 1 that were not blocked were not suitable for a variety of reasons).

1.2 The Works

During the works some changes to the original specifications were made in discussions between the Contractor and Ecological Clerk of Works (ECW). These related mostly to dam spacing and overflows in gullies where water could not be diverted out onto the moor, how to restore the borrow pits and the inability to cut plastic dams to ground level (around 5cms was left upstanding).

1 SSSI –Site of Special Scientific Importance

2, SPA – Special Protection Area, SAC – Special Area of Conservation

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1.3 Monitoring Methodology

There is no generic monitoring protocol to use for assessing the early efficacy of the dams. Thus a recording sheet was prepared and adapted during the monitoring process. The assessment was undertaken by 4 people, two of whom had been the ECoWs, on the 6th March 2012 and included as many of the dams as it was possible to visit during the day. The dams had all been in place for over a year when the monitoring was undertaken. The dams were assessed to record the following parameters:

type of dam: peat, plastic or both materials combined;

if the gully was reprofiled or not;

how much water was held behind the pool, (as a proportion of potential depth of water that could be held behind the dam);

rate of water flow (this would be relative across the dams on one day), trickle, slow, moderate, fast;

any flow of water over, through, under or round the dam;

erosion of the dam or the surrounding ground;

any repairs needed to the dam;

vegetation behind the gully block;

degree of disturbance of adjacent vegetation, either by vehicle tracks or where borrow pits have been created;

additional notes; and

for some dams photographs were taken and the locations recorded.

1.4 Results & Discussion

Forty of the 64 gullies where works were undertaken, were visited and the condition of 360 dams on these gullies was recorded. General notes and comments on specific issues were recorded on another 10 gullies. The analysis has separated the plastic from the peat dams in the first instance.

1.4.1 Plastic Dams

Water levels

Over 50% of the dams held over half the maximum level of water. The water level rather than its area will affect the water table in the adjacent peat, the aim being to raise it. In general terms, however, those dams which are in substantial gullies and are recorded as full to three quarters full do provide significant pools of water in a string down the gully (see Plates 1 and 2 for example).

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Table 1 Levels of Water Held by the Plastic Dams

Water Levels No of Dams Percentage of Total

Full to 3/4 72 32.14

3/4 to 1/2 54 24.11

1/2 to 1/4 40 17.86

<1/4 43 19.20

Nil 15 6.70

Total 224 100

Plastic pilling was also used in a number of small, narrow gullies, especially in the north-eastern section of the moor. Plate 3 shows a typical narrow gully blocked with plastic resulting in a long thin pool along its length. Of the 10 dams surveyed in shallow gullies, only two had the same high level of water behind the block (ie. over three quarters full).

Vegetation Changes

Table 2 shows that over 30% of dams supported S. fallax in the area between one dam and the next and that 16.5% supported S. cuspidatum. The total number of recorded patches of Sphagnum between the plastic dams surveyed in detail was 129. More than one Sphagnum species can occur in any dam section, with additional species including S. subnitens, S. capillifolium and one occurrence of S. palustre. The total area of the Sphagnum patches recorded was 195.37 sq m. This is a significant area in only one year (see Plates 4 and 5 for example).

Table 2 Occurrence of Sphagnum behind the Plastic Dams

Number of Dams in which the Species were Recorded

Percentage of Total Plastic Dams

Sphagnum fallax 73 32.59

Sphagnum cuspidatum 37 16.52

Sphagnum fimbriatum 11 4.91

Total occurrences of Sphagnum species 129

It is likely that some gullies already supported Sphagnum cover, (there are no pre-works data). Two examples of gullies where Sphagnum cover has expanded are G10, where 15 of the 16 dams (93.8%) supported over 1m2 of Sphagnum, and G37, where seven of the 16 dams (43.8%) support Sphagnum, although here the cover is much less (average only 0.1m2).

Plastic Dam Integrity 31(13.84%) of the dams were found to have a flow of water across or around them. The flow was

categorised as a ‘medium flow’ at two sites and in both cases the flow was over the top of the

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dam. Of the others, 18 were classed as ‘slow’ and 11 as a ‘trickle’. No erosion was recorded associated with the plastic piling at any of the dams surveyed in detail. There has been very little problem with high flows of water overtopping or escaping around the sides of the plastic dams and causing erosion in the first year after installation.

Eight dams were found to require repairs and an additional four would benefit if repairs were undertaken but were not essential. In addition, two dams may require works in the near future and need a watching brief.

Vegetation Disturbance One of the major advantages of using plastic piling to form dams is the lack of disturbance to the

surrounding moorland and vegetation. This was clear on Keighley Moor as the materials were flown to site by helicopter and there was very little damage to adjacent vegetation. The analysis showed that of the 224 plastic dam sites, disturbance to adjacent vegetation was considered to be ‘none’ at 187 dams, ‘slight’ at 31 and ‘moderate’ damage at only six. This measure was very subjective but the same pattern was seen across the moor by the various surveyors.

1.4.2 Peat Dams

During the survey, 110 peat dams were recorded in detail and several additional gullies were viewed rapidly which were mainly blocked with peat dams.

Water Levels

Almost 75% of the peat dams (Table 3) were between three quarters full and full and almost 82% were more than half full. This high percentage of dams holding high levels of water is very encouraging and a very visible sign of the changes that have occurred. This provides the potential for water tables to be elevated in the adjacent peat.

Table 3 Levels of Water Held by the Peat Dams

Water Levels No of Dams Percentage of Total

Full to 3/4 80 72.73

3/4 to 1/2 10 9.09

1/2 to 1/4 8 7.27

<1/4 9 8.18

Nil 3 2.73

Total 110 100

Examples of successful peat dams, often in series, creating substantial pools of water behind them are shown in Plates 6-9.

Vegetation Changes

The vegetation changes in the pools formed by peat blocking show a degree of disruption to the existing gully vegetation when the peat is scooped out to form the dam and to the adjacent vegetation in terms of borrow pits and a higher level of vehicle movement across the area. Much

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of the existing vegetation immediately behind the dams has been buried or relocated in the formation of the dam or drowned as the pools fill with water.

The colonisation of species into the pools and flooded areas behind the peat dams is slow. Any existing Sphagnum would have been disturbed by the original works and, therefore, its occurrence in any pool will show new colonisation.

Table 4 Occurrence of Sphagnum behind the Peat Dams

Number of Dams in which the Species were Recorded

Percentage of Total Peat Dams

Sphagnum fallax 2 1.82

Sphagnum cuspidatum 21 19.09

Sphagnum fimbriatum 0 0

Total occurrences of Sphagnum species 26

Less than 2% of peat dam pools contain Sphagnum fallax (Table 4), and a little over 19% contain Sphagnum cuspidatum. No Sphagnum fimbriatum was recorded in the pools behind the peat dams, but three occurrences of other Sphagnum species were noted. Overall, the total area of the Sphagnum was recorded as 19.65sq m. Even allowing for the difference in number of dams studied, it is clear that the Sphagnum is twice as abundant in the areas behind the plastic blocks rather than the peat dams so far. The reasons for this are not clear, although the level of disturbance or changes in water chemistry are possible factors.

The vascular plants generally showed very poor colonisation of the pools within this first year, with only a few shoots of common cottongrass and occasional clumps of hare’s-tail cottongrass recorded.

Dam Integrity Of the 110 peat dams constructed, 49 (44.5%) were found to have a flow of water across,

around, under or through them. This was significantly higher than for the plastic dams. A ‘medium flow’ was recorded at three sites and in all cases the flow was over the top of the dam. Thirty-nine dams were classed as having a ‘slow’ flow (35.45%) and seven (6.36%) as having a ‘trickle’.

The flow in the majority appears to be over the top of the dam whilst water movement around, through and under the dams is lower.

Twenty six peat dams were recorded as having signs of erosion (Plates 10-12), although most is currently minor and sometimes associated with the adjacent land, eg. the borrow pit sites rather than the dams themselves. The rate of flow has, as yet, not caused significant erosion effects.

A relatively high number of dams were found to be very wet, soggy and soft under foot (Plate 12), which is of some concern. Although the dam walls are intact, the wall feels soft and insubstantial. It is possible that the wider spacing of some dams where there is significant water flow has resulted in a larger head of water in the upper pools with no countering force from the pool of water below. The water in the upper pool then forces its way further through the peat dam than anticipated, resulting in wetter peat in the dam wall. What this mean for the longer term integrity of the dams is currently unclear. It may be that additional dams are required to reduce the head of water between the pools. The issue requires discussion between a number of parties on site and appropriate action taken.

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Overall, 16 peat dams are in need of repairs out of the 110 assessed, three of which are not in urgent need of attention at this point.

Vegetation Disturbance The analysis showed that of the 110 peat dams, nine have been constructed with no apparent

disturbance to the surrounding vegetation, 45 had a small amount, 46 had a moderate level and 10 still had a high level of disturbance associated with the dam construction. Plates 13-16 show a range of types and degrees of disturbance associated with the construction of peat dams.

The ten dams with a high level of disturbance were located in four gullies, one of which was also partially re-profiled adding to machine work in the area. As much of the moor is covered in mature or over mature heather, recovery from disturbance will take more than a year.

1.4.3 Combined Peat and Plastic Dams Twenty six dams were constructed combining both peat and plastic in six different gullies where

additional strength was considered necessary in the face of likely water flows.

Nineteen of the dams (73%) had pools three quarters full or more behind them (Plate 17). This was very similar to the peat dam total. Sphagnum was recorded in six dams (23%) and again most of the Sphagnum recorded was S. cuspidatum.

Water was recorded as flowing at twelve of the dams and most was ‘slow’, with only the flow at one dam recorded as ‘medium’. At this dam (Plate 18) the peat on the down side of the plastic has been washed away by the force of the water and is visible in the pool area below. This is the only dam where erosion has occurred. The majority of the flow in these dams again occurs over the top of the dam (eight dams), whilst four slightly leak around the edges and water is recorded as going under three dams and through a further two.

1.4.4 Coir and Heather Bales Coir and heather bales were recommended as water control measures on one area (G1), which

has been damaged by fire. There was a small peat face being eroded by water running off the adjacent area and overland flow was concentrating in a number of newly formed rills.

Figure 1 shows that a considerable number of bales and coir rolls (indicated by the white crosses by G1) were placed to intercept the flow. Plate 19 shows the positioning of the bales with peat build up clearly seen. The bales are therefore functioning well and are holding back water and peat. The bales and coir have reduced the erosive force of the water which would otherwise have caused further erosion.

1.4.5 Gully Re-Profiling

Two gullies - G48a and G48b - were re-profiled as part of the works to reduce the steepness of the slope and allow the sides to re-vegetate, thus reducing peat erosion. They were flask shaped in cross profile with steep, bare peat sides and collapsing edges. G48a was blocked using plastic dams with two combination plastic and peat dams whilst G48b used only peat dams.

The re-profiling of the banks has been well undertaken from a visual perspective and the vegetation replaced on the top of the slopes has generally survived well. However, six of the eight plastic/combination dams on G48a require some minor repairs as the plastic was not taken far enough into the gully edge and water is leaking around them.

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1.5 Conclusions

Raising Water Tables The results and discussion above have clearly shown that the gully blocking undertaken on

Keighley Moor in the winter of 2010/11 has largely been successful as tested against the objectives. It has resulted in the formation of many pools and the inevitable re-wetting of sections of moor adjacent to these pools. Taking all the dam types together, Table 5 shows that irrespective of dam type, 171 dams, just under half (47.5%), had associated pools which were full or three quarters full of water and two thirds of the dams, 238 (66%), were more than half full at the time of the assessment.

Table 5 Levels of Water Held by all Dams

Plastic Peat Dams Combined Peat

and Plastic Dams Overall Total

Water Levels

No of Dams

% of Total

No of Dams

% of total

No of Dams

% of Total

No of Dams

% of Total

Full to 3/4 72 32.14 80 72.73 19 73.08 171 47.50

3/4 to 1/2 54 24.11 10 9.09 3 11.54 67 18.61

1/2 to 1/4 40 17.86 8 7.27 2 7.69 50 13.89

<1/4- 43 19.20 9 8.18 1 3.85 53 14.72

Nil 15 6.70 3 2.73 1 3.85 19 5.28

Total 224 100 110 100 26 100 360 100.00

.

However, a fifth of the dams (72) were less than a quarter full and slightly over 5% were empty. The reasons for the failures need to be fully explored on site to seek modifications to restore them to hold water. Dams not holding water have not generally been included in the ‘repair’ category as their lack of water does not, necessarily, cause problems for the success of other dams in a gully system. There may simply be insufficient water passing down the gully concerned. Only one dam was found to be empty owing to water escaping clearly down a peat pipe on the floor of the dammed space. This was at the bottom of a gully system, thus avoiding impact on the rest of the dams above it.

Increasing the Cover of Sphagnum on the Moor The results (summarised in Table 6) show that Sphagnum has established in many of the pools

and channels behind the dam, although there are some differences between the species and the dam type. Sphagnum fallax and S. fimbriatum were only recorded in the areas of plastic dams. This is thought to be a combination of the type of gullies where plastic was used being a more suitable habitat for these species prior to the blocking and the lack of disturbance to the gully vegetation during construction.

The levels of Sphagnum cuspidatum recorded across the dam types are remarkably similar and show, as is well known, that this species is a good coloniser of open water. It can create a suitable habitat structure in open water to aid the colonisation of other Sphagnum species.

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120108 Penny Anderson Associates Ltd Yorkshire Wate

Table 6 Occurrence of Sphagnum behind all Dams

Plastic Peat Both Total

Number

% of Total

Number% of Total

Number% of Total

Number % of Total

Sphagnum fallax 73 32.59 2 1.82 2 7.69 77 21.39

Sphagnum cuspidatum 37 16.52 21 19.09 4 15.38 62 17.22

Sphagnum fimbriatum 11 4.91 0 0.00 0 0.00 11 3.06

Sphagnum Total Species

129 57.59 26 23.64 7 26.92 162 45.00

It is clear that Sphagnum has increased across the moor since the gully blocking. The current survey has estimated that in the 360 dams surveyed in detail, there is approximately 220sq m of Sphagnum. If it is assumed that if the pattern found is similar in the un-surveyed gullies, approximately 400sq m of Sphagnum could now be on the moor. This is in stark contrast to the statement in the initial surveys that ‘Sphagna are generally sparse’.

Other Objectives

The wingwalls (plastic piling forming shapes to fit the location varying from straight to matching a peat edge shape), which have one of two functions depending on the specific site location; holding back water on patches of blanket bog and/or blocking known peat pipes, are generally working well. One or two may require some modifications but no serious concerns about these experimental blocks have arisen from the monitoring.

The re-profiling of two gullies has gone well and combined with the blocking of the gullies means that a significant area of bare peat is no longer in contact with flowing water.

Recommendations There is a need to re-visit the site with the contractor and discuss the repairs suggested in this

report. Also the remaining gullies need to be re-visited to ensure that all problems are identified during the defects liability period of the contract. Some of the repairs are straight forward, such as extending plastic piling to prevent water from the dams creeping around the edges and potentially causing erosion. Other repairs are more complex and will need debate and discussion. Additional dams may be required to reduce the head of pressure or additional works are required to strengthen the existing dams where they are too wet. Additional dams could be peat, plastic or a combination of these. Stone dams are also a possibility and this is recommended where the peat has washed away at one dam site.

r2012 Keighley Moor Dam Efficacy Monitoring

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Title:

Project Name

Discipline

OriginatorDrawn By Date

PAA Ref.

Scale Drawing No.

Revision

Penny Anderson Associates Ltd,Parklea, 60 Park Road,Buxton, Derbyshire, SK17 6SN.Telephone 01298 27086

0 20 40 60 80 10010

Metres

´British National Grid

Projection: Transverse MercatorFalse Easting: 400000.000000

False Northing: -100000.000000Central Meridian: -2.000000

Scale Factor: 0.999601Latitude Of Origin: 49.000000

1:3,500

Keighley Moor Dam Efficacy Monitoring

Ecology

Figure 2

MAR 2012

A

ISO A3

G:\YOWA02_KeighleyMoor_2010\Maps\Figures

JL KL

Dam WorksUndertaken by

Dinsdale Moorland Services 2010/2011

Legend

Ë Blocking Works Completed Dinsdale 2010/11 (693)Gullies to block (recommended Dec 2010) 73All gullies identified on Lidar DTM dataSite boundary

Yorkshire Water PO Box 52BradfordBD3 7YD

Yorkshire Water mapping is based upon OrdnanceSurvey map data with the permission of the Controllerof Her Majesty’s Stationary Office, (©) Crown Copyright.Licence No.1000019559

Gully Blocks on Keighley Moor 2012 Gully Blocks on Keighley Moor 2012 Plastic Dams - Plates 1-5 Plastic Dams - Plates 1-5

Plate 1 G10 - looking up gully with Sphagnum cuspidatum in closest pool, overtopping the dam.

Plate 2 G37 looking up the gully.

Plate 3 Typical plastic dam in narrow gully (G47). Water filled channel obvious.

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120108 Yorkshire Water March 2012 Keighley Moor Dam Efficacy Monitoring

Plate 4 G10a. Substantial Sphagnum cover in pool immediately behind dam.

Plate 5 G39 - Plastic dam with frequent and locally abundant Sphagnum in wet areas in front and behind dam.

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Peat Dams - Plates 6-8 Peat Dams - Plates 6-8

Plate 6 G24a down system. Good example of a peat dam holding water.

Plate 7 Bottom peat dam in Gully 38. Holding water, full to three quarters full, but no Sphagnum.

Plate 8 G40 looking down gully. Water in pools quite deep but no vegetation.

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Plate 9 Top dam in Gully 38. All the dams are holding water and are full to three quarters full. Six out eight are supporting Sphagnum species.

Plate 10 G48b. Erosion at west side of dam. Needs repairing.

Plate 11 G48b. Dam not high enough to contain flow, leaking from west side and through the dam wall.

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Plate 12 Gully BB. Small amount of Sphagnum in pool and rare shoots of common cottongrass. Dead heather around margins. This pool is leaking over the front and the dam wall is very wet and soggy.

Plate 13 G27. Borrowpit area in the foreground. Pools have formed but no erosion problem.

Plate 14 Disturbed and uneven turves on a peat dam G23. Heather turves used to cover the dam are dying.

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Plate 15 Across G32. Damage to heather at top of the gully from peat excavation for dams and excavator tracks.

Plate 16 Damaged heather by Gully DD caused by excavators tracking over old heather.

Peat and Plastic Dams – Plates 17-18

Plate 17 Series of peat and plastic dams in G17, looking down the system. All are over half full with two pools supporting Sphagnum.

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Plate 18 G36 washed out Dam. Peat has washed into the pool below.

Heather Bales – Plate 19

Plate 19 Heather bales at G1 used to intercept overland flow (poor light at dusk).

YORKSHIRE WATER KEIGHLEY MOOR DAM EFFICACY …

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